In recent years, with the developments in information communication apparatus, shortage of the capacity of signal lines within such apparatus becomes problematic. For solving the problem, the replacement of a part of electric wiring made of copper in the printed circuit board within the apparatus by an optical waveguide and the use of optical signals in place of electric signals come under review. Since high-density optical wiring is required to be housed in a limited space, the following is examined in the apparatus. That is, in the same manner as in ICs and multi-chip modules, a photoelectric element such as a laser diode or photodiode is mounted on a surface of a substrate, and optical wiring layers are stacked on the same substrate as the electric wiring substrate. Such optical surface mounting circuit substrate is disclosed in, for example, Japanese Patent Publication Nos. H05-72429A and 2004-94070A.
In an optical-electrical wiring substrate in which an optical waveguide is stacked on the same substrate as an electric wiring, high-density mounting can be achieved. However, in order that an optical waveguide may be optically connected to a photoelectric element such as a laser diode or photodiode, an optical path switching technology for switching an optical path of the optical waveguide by an angle of 90 degrees is required.
In Japanese Patent Publication No. H05-34526A, for example, as illustrated in FIG. 1, a groove 4 extending toward an inner side from a surface 3a is formed in a substrate having formed therein an optical waveguide 2 by machining and etching. This groove 4 is made oblique by 45 degrees relative to the substrate surface 3a. As a result, an end face of the optical waveguide 2 faces the groove 4, and an optical reflecting mirror is formed on the end face of the optical waveguide 2. Light A propagating through the optical waveguide 2 is reflected by a wall surface 4a of the groove 4, namely, by the optical reflecting mirror, and propagates toward the surface 3a of the substrate to enter a photoelectric element 5 on the substrate surface.